(Not applicable.)
The present invention relates to a device for regulating the pressure and/or the flow of a gas stream, which device comprises a housing which is provided with a pressure-regulating chamber, at least part of whose wall comprises a diaphragm, which diaphragm is subjected, on the side remote from the pressure-regulating chamber, to an adjustable prestressing force, the pressure-regulating chamber comprising an inlet opening for a gas and an outlet opening for a gas, it being possible for at least one of the openings to be completely or partially closed off with the aid of the diaphragm. This means that the extent to which the diaphragm bends is dependent, on the one hand, on the instantaneous pressure in the pressure-regulating chamber and, on the other hand, on the stress which is applied to the diaphragm with the aid of the prestressing means, wherein the diaphragm is actively connected to a pressure chamber for a gas, which pressure chamber is provided with has an inlet opening for a gas and an outlet opening for a gas for setting the pressure in the pressure chamber for the purpose of applying the prestressing force.
A device of the abovementioned type is known in the prior art. The device may be used, for example, to regulate a gas stream which is at a relatively high pressure down to a gas stream at a lower pressure. The position of the closure member is linked to the bending of the diaphragm. Consequently, the pressure of the gas stream which leaves the pressure-regulating chamber via the outlet opening will be determined by the position of the diaphragm in a starting position. The known device can be used to reduce the pressure of a gas stream to a desired level. The pressure of the gas stream which will leave the pressure-regulating chamber at the outlet opening will be dependent on the size of the inlet opening which is left open by the closure member. The more the closure member closes off the inlet opening, the lower the pressure flowing out of the outlet opening of the pressure-regulating chamber will be.
The above mentioned device is (i.a.) known from U.S. Pat. No. 4,798,521. From this document a device is known for regulating the pressure in a container. In addition to the mentioned elements, the known device comprises means for measuring possible differences in the pressure in the pressure chamber and the device""s outlet opening, which differences can used for regulating the pressure in the pressure chamber.
An important drawback associated with devices known from the prior art is that it still is impossible to accurately set the position of the diaphragm. In practice the switching time of the valves inside the inlet opening and the outlet opening will not be infinitesimal. There will always be a physical limitation which limits the accuracy of the control.
The object of the present invention is to provide a device of the type mentioned in the introduction with which it is possible to accurately set the position of the diaphragm. It is also desirable for it to be possible to adjust a position of the diaphragm once it has been set, in a relatively simple manner.
These objects are achieved, in the present invention, in that the inlet opening is provided with a flow restriction. Therewith it is possible that outlet opening is provided with a flow restriction.
The use of a pressure chamber in which a gas is kept under pressure allows the position of the diaphragm in the starting position, and therefore the position of the closure member in the inlet opening of the pressure-regulating chamber, to be adjusted with the aid of a gas pressure. By increasing or reducing the pressure in the pressure chamber, the position of the diaphragm can be fixed as desired.
Because of the presence of the restrictions at both the inlet opening and the outlet opening it is possible to control the flow to and from the pressure chamber with a much higher accuracy then before.
According to the invention it is further possible that the side of the diaphragm which is remote from the pressure-regulating chamber adjoins the pressure chamber. Therewith it is possible that the inlet opening and the outlet opening of the pressure chamber are provided with a remotely controllable shut-off valve.
Therewith the position of the diaphragm can be altered by altering the pressure in the pressure-regulating chamber.
These measures ensure, in a very simple manner, that the pressure in the pressure chamber can be increased or reduced. The remotely controllable shut-off valves allow the setting of the pressure in the pressure-regulating chamber to be coupled, for example, to measuring means which are accommodated elsewhere in the device.
According to the present invention, it is possible for the device to be provided with means for measuring the pressure of the gas stream, which measuring means are arranged in the vicinity of the outlet opening of the pressure-regulating chamber. It is also possible for the device to be provided with means for measuring the pressure of the gas stream, which measuring means are arranged in the vicinity of the inlet opening of the pressure-regulating chamber. In this case, it is advantageous for the device to be provided with regulating means which are actively connected to, on the one hand, the means for measuring the gas pressure and, on the other hand, the remotely controllable shut-off valves of the pressure chamber.
These measures ensure that the pressure or the flow of the gas stream which leaves/flows into the pressure-regulating chamber can be monitored. By additionally coupling this pressure measurement to the remotely controllable shut-off valves, it is possible for any deviations in the measured pressure of the gas stream to be directly translated into a change in the position of the diaphragm.
According to the invention, it is also possible for the diaphragm to be connected, via a coupling member, to a second diaphragm, the said second diaphragm adjoining the pressure chamber, and that side of the diaphragm which is remote from the pressure-regulating chamber adjoining a second pressure chamber, the pressure-regulating chamber being in communication, via a restriction, with a feed line for a gas, and the second pressure-regulating chamber being in open communication with the said feed line.
This measure allows the present invention to be used for setting a diaphragm, with both its sides adjoining a feed line for a gas stream. The first side of the diaphragm adjoins a closed space which contains an outlet opening and is connected to the feed line via a restriction. The other side of the diaphragm adjoins a closed space which is in free communication with the feed line. If flow takes place from the feed line, via the restriction, to the outlet opening of the closed space on the first side of the diaphragm, the presence of the restriction will cause there to be a pressure difference across the diaphragm. This pressure difference determines the position of the diaphragm and hence the extent to which the outlet opening is closed off. The equilibrium position about which the diaphragm will move can be set, by means of the measures described above, with the aid of the said pressure chamber, it being possible to vary the pressure in the pressure chamber. At least one wall of the pressure chamber is formed by a second diaphragm which is connected, via a coupling member, to the diaphragm which is connected on both sides to the feed line.
The present invention also relates to a gas chromatograph provided with the above mentioned device.
The device according to the present invention is especially suited to be used in a gas chromatograph. Firstly because at both sides of the diaphragm a gas is present, diffusion through the material of the diaphragm will be limited to a minimum. Further it is possible to connect both the inlet opening of the pressure-regulating chamber and the inlet opening of the pressure chamber to one and the same feed line. That means that on both sides of the diaphragm the same gas will be present. In the gas chromatograph it is possible to add a substance to be examined to the gas flow when the pressure of the gas flow has been decreased from a relatively high pressure to a relatively low pressure, i.e. downstream of the device according to the present invention. The result of this will be that possible loss of material to be examined will be prevented.
In a second aspect, the present invention relates to a method for regulating the pressure or a flow of a gas stream, in which the gas stream to be regulated is fed from an inlet chamber, via an inlet opening, to a pressure-regulating chamber, at least part of whose wall is formed by a diaphragm, the pressure in the pressure-regulating chamber being regulated by adjusting the size of the inlet opening of the pressure-regulating chamber with the aid of a closure member which is actively connected to the diaphragm in such a manner that a change in the level of displacement of the diaphragm causes a change to the extent to which the closure member closes off the inlet opening, the diaphragm being subjected to a prestressing force, with the aid of which a specific positioning is imposed on the diaphragm.
The method according to this invention is characterized in that the said prestressing force is applied by a pressurized gas in the pressure chamber, the starting position of the diaphragm being set by setting the pressure of the gas in the pressure chamber.
According to the present invention, it is possible for the gas stream to be discharged from an outlet opening of the pressure-regulating chamber. In this case, it is advantageous for the pressure of the gas stream to be measured at least periodically in the vicinity of the outlet opening of the pressure-regulating chamber, and for the measured value to be compared with a desired value which is dependent on the starting position of the diaphragm, and for the pressure in the pressure chamber to be increased or reduced on the basis of this comparison by feeding or discharging gas to or from the pressure chamber.
This measure makes it possible to keep the pressure in the gas stream which leaves the pressure-regulating chamber as close as possible to the desired value. In principle, the device is designed in such a way that any deviations from the desired pressure in the gas stream emerging from the pressure-regulating chamber caused by variations in the position of the diaphragm can be eliminated by the device itself. Any undesirable residual variations can be effectively eliminated by means of the method according to the invention.
Furthermore, it is possible, according to the invention, for a volume of gas to be fed to the pressure chamber, during or after which process a different volume of gas is discharged from the pressure chamber.
The effect of this measure is that during use of the device according to the invention there is no problem with so-called dead spaces. If an insufficient volume of gas were to be fed to the pressure chamber, the diaphragm might react in a non-linear manner to this addition of gas. By ensuring that the volume of gas which is supplied is always greater than a specific threshold, and that a certain volume of gas is discharged during or immediately after this volume of gas has been supplied, it is ensured that, on balance, small volumes of gas can be fed to the pressure chamber, in other words that the pressure in the pressure chamber can be adjusted very accurately without there being problems with dead spaces.
According to the invention, it is advantageous if the pressure in the pressure chamber is allowed to gradually increase or decrease.
For certain applications, it may be advantageous to allow the pressure of the gas stream which leaves the pressure-regulating chamber to gradually increase or decrease. For example, in the case of a gas chromatograph, it may be that in the event of variations in pressure, different elements are separated out of the gas stream in a column which may be positioned in a line which is connected to the device according to the present invention. If the pressure in the pressure chamber is now gradually varied, the pressure of the gas stream leaving the pressure-regulating chamber will also vary. These variations may benefit the separating capacity of the column.